Hi and welcome to the forum first.
I have a 2010 318SAB Cougar but the remote should work the same way.
First make sure you have a new battery in the remote.
Press the SEL button to turn on remote. You than press the SEL and one of the up/down arrows to access the menu.
You than can scroll thru the menu to activate the function you want such as extend/retract main slide.
The remote will turn its self off with no activity after a few minutes.
If you cannot get the remote to work than the receiver/remote may have failed. If this is the case see the selling dealer/Keystone for help with this.
Do you have acopy of the O and M Guide?
If not here is the link.
http://www.keystonerv.com/?page=service
The guide is at the bottom of the page.
Jim W.